1. Field of the Invention
The present invention relates to a key assignor for use in electronic musical instruments.
2. Description of the Prior Art
In electronic instruments such as an electronic organ having a number of key switches, and in case of transferring opening and closing informations of switches to a desired circuit, it is uneconomical to provide a direct connection between the switches and the circuit because a quantity of wiring becomes massive. Further, since the number of connection pins is limited in order to integrate the circuits, an increase in the number of pins impairs integration. Moreover, in terms of limitation relative to sound source of 10 fingers and two feet as seen in the electronic organ, the number of sounds to be produced is twelve, and therefore, twelve sound sources will suffice. It is apparent from the above that the opening and closing information of the switches may be put in twelve channels to decrease the number of circuits, which reduces cost and makes it possible to provide integration.
In the past, a system has been used, wherein key switches are successively scanned by a predetermined clock so that the on-off information is formed into TDM (Time Division Multiplication) signal or PCM (Pulse Code Modulation) signal in synchronism therewith, and the key code is multiplied and put in desired circuits. However, the aforesaid system requires one scanning section for scanning all of the switches in order to feed the opening and closing information of all of the switches. For example, where 154 key switches composed of 61 upper keys, 61 lower keys, and 32 pedal keys are scanned at a time slot of 10 .mu.s (micro-second), it requires 1.54 ms (milli-second) for one scanning, and time displacement relative to those switches turned on after scanned has been encountered. Further, it is of no use to scan all of the switches to feed information other than is needed. Obviously, if a change in on or off is delivered by transferring the on state, the quantity of information will be decreased. It may readily be discriminated in normal contacts that distinction of on and off will be in the order such that the odd contact is in on state while the even contact is in on state, such as on followed by off and off followed by on.